The behavior of ultra high molecular weight polyethylene after implantation in total joint prostheses is to be evaluated by total joint simulation in bovine serum, mechanochemical studies, and evaluation of clinical failures. The wear process will be characterized by scanning electron microscopy of the wear surfaces and wear debris, molecular weight distribution studies of wear surface and interior material and wear debris, quantitative recovery of wear debris, and other techniques which measure chemical, structural and physical changes in polymers. The effect of uniaxial and biaxial stress on chemical reactivity and absorption of serum components, and on mechanical properties will be studied. The range of properties and behavior of commercially available ultra-high molecular weight polyethylene, as marketed for total joint replacements, will be studied and related to the service behavior of this material. The goal is to identify the basic mechanisms of deterioration in vivo, to develop a long-term prognosis for this material, and to obtain the necessary basic knowledge to optimize its properties.